560 



Fishery Bulletin 93(3), 1995 



would have two potentially desirable consequences. 

 First, it would distribute effort more evenly across 

 sites with the entire range of growth rates. This 

 would occur because more abalone could be collected 

 from sites where they grow slowly, and less would be 

 available at sites where they grow quickly. Follow- 

 ing the progressive increase in length limit during 

 the 1980's, most fishing became concentrated at sites 

 where abalone grew quickly (see also McShane, 1992). 

 As described above, the length limit at these sites was 

 also lower than appropriate, which in combination with 

 the intense fishing effort, so that populations at sites 

 where growth was fast were exploited at considerably 

 higher rates than those for other populations. 



The second desirable consequence of enforcing a 

 width limit would be to allow the collection of aba- 

 lone from sites that are presently unfished because 

 abalone grow very slowly and few reach the mini- 

 mum legal length (i.e. as stunted abalone). If an ap- 

 propriate width could be chosen, more abalone would 

 be available for collection at sites where they grow 

 slowly, making it viable for divers to visit such sites. 

 There is some evidence to suggest that growth rates 

 of individuals at sites where they appear stunted are 

 limited by a lack of available food (Shepherd and 

 Hearn, 1983). By removing individuals, more food 

 may be available to those that remain and their 

 growth rates may, in turn, increase. 



Considering the frequency of studies reporting 

 covariation in growth and morphology of abalone, we 

 suggest that alternative size limits appear to have 

 the potential to improve the management of many 

 abalone fisheries. The intense spatial variation in 

 growth and related differences in morphology of 

 Haliotis rubra in NSW, and the ease with which shell 

 width can be measured, make a size limit based on 

 width a potential alternative to the present length 

 limit. The application of a width limit would allow 

 abalone that have grown at different rates to be har- 

 vested at different lengths, essentially enforcing dif- 

 ferent length limits over very small spatial scales. 

 As a consequence, the potentially damaging imbal- 

 ance in exploitation rates among sites with different 

 rates of growth in length would be avoided. 



Acknowledgments 



DGW and NLA would like to acknowledge the fore- 

 sight of GH in the initiation of the tagging program 

 and in the subsequent retention of recaptured shells. 

 Others who helped tag and recapture abalone include 

 T Butcher and J. Matthews. R. I. C. C. Francis pro- 

 vided us with Grotag, and G. Gordon and M. Krogh 

 helped with programming. N. Bentley, P. Brett, P. 



Fairweather, D. Ferrell, R. I. C. C. Francis, and W. 

 Nash helped improve various drafts of the manuscript. 



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